In general, to obtain a thermal recording sheet, a colorless or pale colored electron-donating dye and a color developer (an electron accepting material), such as a phenolic compound, are individually pulverized to fine particles, mixed with each other, and a binder, a filler, a sensitizer, a slip agent, and other additives are added to obtain a coating color, which is coated on a substrate such as paper, synthetic paper, films, plastics, or the like. The coated sheet is color developed through an essentially instantaneous chemical reaction which is induced by heating with a thermal head, a hot stamp, laser light, or the like to obtain a visible record. The thermal recording sheet can be used in a wide variety of applications, such as measuring recorders, terminal printers for computers, facsimile machines, automatic ticket vending machines, bar-code labeling equipment, and the like.
Urea compounds are well known as electron accepting materials which are commonly used as developers in thermal recording media. U.S. Pat. Nos. 5,470,816, 5,656,569, 5,811,369, and 6,927,007 describe thermal recording media which can include such urea compounds. In any case, the thermal recording media should include a developer which allows for high efficiency and good reactivity while meeting additional desired properties which can include appropriate thermal response, heat resistance, water resistance, oil resistance, plasticizer resistance, and low background color.